CZ301895B6 - Security device - Google Patents

Abstract

In the present invention, there is disclosed a security device comprising a holographic optically variable effect generating structure (1) having at least two discrete sections (2). The sections (2) generate in response to white light illumination (51) an optically variable image (3 through 5) consisting of at least two defined graphical elements located at or near an image plane either on or adjacent to the plane of the device. In response to coherent illumination (6), the sections (2) generate at least two discrete covert images (7 through 9), in the form of indicia, whose image planes are located at a distance away from the real plane of the device. The covert images (7 through 9) are reconstructed at different angles to a normal to a substrate (1) supporting the device such that the covert images (7 through 9) are spatially separated on their image plane, the covert images (7 through 9) being non-visible under white light illumination.

Description

Technical field

The invention relates to a security device used to secure documents and other valuable items against their fraudulent reproduction, falsification and the like, the security device comprising a holographic structure generating an optically variable effect.

BACKGROUND OF THE INVENTION

Many security devices are based on the use of optically variable effect generating systems that generate holograms and the like, since they are difficult to produce. Examples of such holographic systems and techniques used to make them can be found in EP-A0548142, EP-A-0632767 and WO-A-99/59036, all owned by De La Rue International Limited. The theory set forth therein and the other patents referred to therein are incorporated herein by reference. WO-A-92/09444 is also included herein as part of the prior art, which shows how to achieve a better durability that is safe and simple in proving the authenticity of an optical microstructure image element to visually prove the authenticity of a banknote. Certain diffraction grating security devices already exist, as described, for example, in EP-A-0105099, which discloses a security device generating the effect of an apparent movement and consisting of flat diffraction grating surfaces oriented in different directions along a certain path, each refracting a beam of incident light in a different direction, although it should be noted that they are purely diffractive grating devices, where each segment is a purely diffractive grating and is therefore not able to create as a secret feature an image that would be off-plane in coherent illumination.

Regarding earlier machine-readable or coherently visible holographic security systems, we would like to refer to EP-A 0548142 concerning technologies whereby a hologram for proof can produce an off-plane image, although we would like to show here that in this case the removable structure of the formula designed in such a way as to remain completely obscured from visual observation by the hologram observer and actually consisted of superimposed weak diffraction gratings that did not produce an image centered off the image plane. DE-A-3840037 shows an example of a visual security hologram comprising a superimposed additional laser transmitted hologram intended to produce a planar image that can be detected by laser light using a machine reader or visualizer and will not be recognizable under normal illumination.

There is a continuing need to increase the safety of such security devices while allowing them to be readily proven.

US-A-5825478 discloses a system and method for determining which of a plurality of visually indistinguishable objects has been labeled with a hidden indicator, wherein a portion of the surface of each of the first type objects has a hidden holographic indicator that is exposed to view. of a predetermined wavelength.

SUMMARY OF THE INVENTION

According to the present invention, the security device comprises an optically variable effect generating structure, said structure comprising at least two discrete portions which, in response to white light illumination, generate an optically variable image consisting of at least two defined graphical elements placed on or in the near the image plane and which at

At least two discrete hidden images, in the form of indicia, whose image planes are located at a distance from the actual plane of the security device, the hidden images reconstructed at different angles to the perpendicular to the substrate supporting the device, in response to coherent illumination so that these hidden images are spatially separated on their image plane and these hidden images are invisible when illuminated by white light.

In this context, we understand the holographic structure generating the optically variable effect of any fractional device having the property of producing a first visual localized graphic image near the actual plane of the visual observation device and which also produces off-plane and concealed laser verifiable image (instead under coherent light. Such a structure can only be created by holographic means or by computer calculation and by directly writing the desired band pattern of the structure, which is a slower and more time-consuming method of creating such an element.

A particularly useful form of an optically variable effect generating holographic structure is one in which the sensing directions of the visual optically variable image are designed to produce an apparent movement effect when the device is tilted about a particular axis.

The optically variable effect generating structure may be formed as a single continuous structure 20a.

The new holographic security device comprises a structure which, in the plane of the image adjacent to the structure, produces at least two localized optically variable graphic images in response to white light illumination and at least two hidden images separated from the image plane in response to coherent illumination and positioned at different angles to the perpendicular led to a substrate supporting the device. Hidden images will usually be separated by a distance of about one-half their size. Thus, under normal white light illumination, an observer will see a typical optically variable image such as a hologram or diffractive effect consisting of at least two or more Parts, but in a coherent illumination such as laser light, the observer will see two or more different hidden images.

These hidden images will preferably be in the form of graphic elements, a logo or alphanumeric characters, which may typically relate to a given type of goods or document equipped with a security device. The visual optically variable images will also preferably be in the form of small defined shapes and indicia.

In this preferred case, hidden images are visible to the naked eye only if they are reconstructed by the coherent laser illumination of the device, although they could also be produced at a certain wavelength outside the visible area for machine detection.

In one embodiment, the optically variable effect generating structure, in response to white light illumination, produces two or more graphic images or shapes that appear to move when the device is tilted. In this context, we distinguish between the apparent three-dimensional appearance of the hologram and something similar to a motion effect such as a lateral motion created by different angles of diffraction between the elements.

In this embodiment, each element of the structure producing the holographic optically variable effect is suitably formed as a single structure typically having a maximum lateral dimension not exceeding 1.5 mm. The maximum lateral dimension should not be less than 0,5 mm and preferably within the range of 0,5 to

0.75 mm, at least two such elements repeating different hidden images in the device in different directions should be provided.

Restoring hidden images can be improved by providing a certain number of pairs or sets (three or more) of these parts, each element of a particular pair or set being arranged in such a way as to produce the same hidden image as another element in response to coherent illumination. (other elements) of said pair or set. In this case, the individual elements must be positioned sufficiently close to each other to be in the diameter of the illuminating, coherent beam of beams so that the entire hidden message can be reproduced. Typically, the illuminating beam has a diameter of about 2 or 3 mm using a laser pointer or other similar device.

In order to increase security by increasing the complexity of the overall device and to conceal the presence of this new optically variable effect holographic structure, this holographic and optically variable effect structure may also be placed in a set of other optically variable effect generating structures designed to produce images or effects visible only in bit-light, in which these single and other optical effect structures, when tilted under white light illumination, cooperate to produce a moving image effect.

Thus, an untrained observer will observe a moving image when illuminated by white light and only after illuminating the correct set of structures producing optically variable effect by coherent light will he be able to detect hidden images. Under normal "white light" illumination, it will not easily be apparent that there is a difference between all structures and that other hidden images are contained in this device.

In another embodiment, the portions of the structure create optically variable effect as discrete spaced surfaces.

As in the first embodiment, pairs or sets of surfaces may be provided to improve reproduction of hidden images, and each surface may typically have a maximum lateral dimension not exceeding 1.5 mm. The maximum lateral dimension should not be less than 0.5 mm and preferably within the range of 0.5 to 0.75 mm.

This second embodiment is particularly useful when the structure, in response to white light illumination, produces an image that moves when the device is tilted. This combination of devices is particularly difficult to reproduce, but it is easy to prove its authenticity.

This holographic structure producing an optically variable effect and showing a hidden off-plane image exists as a holographic structure comprising two image planes, one visual image plane for viewing in white light, and an off-plane image plane that is visible when the device is illuminated with coherent light.

The shape of these discrete portions, preferably graphical elements, must form a focal point very close to the plane of the hologram surface, while the information encoded therein forms a focal point (or image) far enough away from that surface plane to require coherent, such as laser illumination, so that they can be seen and hence verified. Under illumination by said light source, each graphic element will reproduce its particular information element in a specific and unique angular direction, so that when a complete laser-verifiable observation element is located in its imaging or focal plane, each information element will have its own well-defined and separate zone or observation area.

Thus, for example, hidden images may define machine readable patterns such as a particular bar code, each graphic element corresponding to a corresponding portion of the bar code.

In some cases, all discrete portions will have the same simple geometric shape that is not related to or borrowed from the main holographic image graphic composition, such as circles (dots), squares, or rectangles. However, the area of the above graphic elements should not exceed 3 mm ² .

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In other cases, the graphic elements can be hidden from the observer by being completely integrated into the main holographic image structure. This is achieved by first selecting a smaller (in terms of area) but otherwise complete graphic element or graphic unit that forms part of the holographic image structure - preferably a graphic structure element that is repeated as part of the kinetic or lenticular movement sequence and this the graphic element is then subdivided into two or more discrete portions. One information unit will be holographically encoded in each of these graphical parts, which will include a laser verifiable feature.

Typically, graphical elements such as alphanumeric characters and the like are used as indicia.

The structure producing the optically variable effect is best formed as one continuous structure. However, elements could be defined by separate substructures with gaps between them that will not bend light. In this case, these elements could be created in separate steps.

Typically, the device may be incorporated into a security hologram or security holographic steps of the structure (e.g., hologram, kinegram, pixelgram, point matrix structure, stereogram, etc.). In this case, the part of the structure that additionally responds to coherent illumination preferably has a grid frequency lower than that part of the structure that produces an image or effect visible only in white light.

Alternatively, it could be used as a stand-alone security optical microstructure where only a small area is available, such as a banknote security strip, where this device could provide both publicly recognizable animation or apparent movement and in addition a unique hidden security device visible only by laser. A particularly useful application of this new security device is the possibility of additional public recognition, since hidden images allow public recognition and security devices for use on banknotes and potentially on other valuable documents where the optical microstructure is applied to a non-smooth and uneven paper substrate. considerably greater resistance of the laser-verifiable structure to paper roughness and crease than previously known techniques because it is located on a small area. It is also intended to be used as a security measure against counterfeiting to secure plastic cards on branded goods.

Another possible use of this device could be a trademark symbol that is laser verifiable. For example, many security holographic devices could include the same, seemingly easily recognizable, publicly recognizable element embedded in a surface, either as a set of dots or graphics to create a simple visually evident motion effect (eg, a set of 2 lines and 3 points moving towards each other) tilting), which would become a standard device which, however, could, under coherent laser illumination, reproduce completely different laser-visible messages that can only be detected under coherent illumination.

This could be used to update all forms of security hologram and bending grid security devices, such as point matrix devices and more specialized techniques such as Kinegram (OVD Kinegram Corp.) and Exelgram (Commonwealth Scientific Industrial Research Organization) (CSIRO) ), Australia), which would apply to all forms of security documents and security stickers, including those used for trademark protection and banknote protection, such as security strips and holographic strips and inserts affixed to paper and other pads and substrates.

A particularly useful potential application could be the window strip, which is commonly used for banknotes and other securities where holographic strips are available, but the viewing area available in each window severely limits the degree of security that can be incorporated into a holographic image. This small area of the window is for revealing the visual

Thus, it makes it difficult both to create an effective, simple visual publicly recognizable security device and to incorporate an additional optical security device in the form of machine-readable or laser-readable images. The present invention would allow the strip to include a simple, publicly verifiable switching or moving pattern (potentially, however, quite simple to be imitated by a dot matrix formula) that could also reproduce a laser-verifiable security hidden element. Similarly, this element could be incorporated into a repeating dot pattern or graphic pattern on a banknote or pad to enhance the security of optical microstructures of banknotes, as the technique disclosed herein is much more resistant to crease, paper roughness and other degradation in use than drives. published devices

Another important but somewhat different application of this type of improved machine verifiable device would be an improved banknote security device based on the theory of WO-A92 / 094444. Another safer form of publicly recognizable security hologram security device on banknotes is the use of repetitive elements as in WO 92/09444, but instead of processing them in pairs and reproducing many times a repetitive simple rebuild image, one or both of these holographic elements are used to provide an apparent movement effect. such as running or turning), which would be more difficult for a holographic laboratory to falsify and would also provide a useful holographic, publicly recognizable or un20ed device. Within the run of repeating elements that would not seem to overlap or overlap only slightly to provide, for example, a three-dimensional depth effect, or a simulated tilting effect, some or all of these elements could contain laser-verifiable elements as described in this technique which would exhibit improved durability and visibility under relatively simple coherent lighting conditions, for example using a laser pointer.

A further advantage of preferred embodiments of the present invention is that they potentially provide an additional third level of security control for the security devices, different from prior systems. The first layer of security is an animated visual image created for visual observation potentially as part of the security hologram structure. The second level of security is the presence of a hidden, laser-verifiable message that is simply detected by a relatively unprofessional observer using a simple coherent light source, such as a laser pointer and screen. Another third level of security would be to analyze the reproduction angles and probably the composition levels of the laser-visible image. This could be done for a more sophisticated security check using a laboratory or machine reading device or a viewing device designed to identify the reproduction geometry of laser verifiable elements more accurately than would be possible using the single laser pen method to provide additional typical security check.

DETAILED DESCRIPTION OF THE INVENTION

Some examples of security devices 1 according to the invention will now be described with reference to the accompanying drawings, in which Fig. 1 shows a schematic representation of a first embodiment of the security device I under white light illumination; Figure 2 shows various images that could be produced using the technique of Figure 1; Fig. 3 shows a first embodiment with laser illumination: Fig. 4 shows the production of one structure for use with the first embodiment: Figs. 5A and 5B illustrate a second embodiment with white light and laser light illumination; and Figs. 6 and 7 show schematic views. similar to FIG. 3, of other examples of laser illumination devices.

In a first embodiment, the device was combined into a relief hologram for security use.

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The security device 1 in the form of a standard, rainbow, embossed security hologram (FIG. 1) optionally comprising additional holographic security elements (not shown) has 6 discrete sections 2 in the form of additional points incorporated into one surface of the structure, in this case constructed as a reasonably different area. In this case, discrete sections were used

2 in the form of small dots (in the range of 0.25 to mm), although a series of graphic elements or other symbols such as the text of a particular word could be used. When tilting the security device 1 in the form of a hologram, in this case from left to right, under white light 51 or under normal ambient light, the holographic reproduction from the discrete sections 2 in the form of dots is designed to appear to move relative to each other in a very specific way, in this case too, these six points were arranged in 2 rows of three and three display pairs of points. The direction of the holographic reproduction from the discrete point-shaped sections 2 has been arranged so that the discrete point-shaped sections 2 seem to move toward and away from each other as the hologram is tilted horizontally from left to right as schematically represented by optically variable images denoted by reference numerals 3, 4 This apparent movement provides an animated publicly recognizable diffractive element with images located near the surface of the security device.

Giant. 2 illustrates various other types of image that could be used instead of the conventional dot images shown in FIG. 1. In these cases, a series of letters are shown, these letters appearing in a sequence as the security device also tilts. . This sequence may be linear (Figs. 2A and 2B), in the form of rotation (Fig. 2C), in the form of unfolding, in other words, consecutive letters appear further away from the center point (Fig. 2D), or in repeated form 2E.

In this preferred case, at least three directions of reproduction as shown in Figure 1 will be used, and typically three or more pairs or sets of dots or graphic elements with each member of a pair reproducing in the same direction will constitute a useful minimum requirement to create an effective public a recognizable security device i for providing also effective laser reproduction and resistance to damage on any particular patch, as well as some degree of ease of arrangement for laser reproduction.

The second element of this new security device is only visible under certain coherent illumination 31 in the form of laser illumination, and in this case we have designed the hidden elements visible only through the laser. They are designed in such a way that they can be very easily verified by a non-trained person verifying their accuracy by simply illuminating said element with a beam of 6 rays (Fig. 3) using a diode laser pointer or laser pen or similar device and displaying a very small screen 7 out of the plane of the hidden graphic image, although it would of course be possible to design for this purpose some special machine reading device, ie. authentication box. Only the sheet could represent screen 7

4ů of paper. Each element of the device under coherent laser light illumination 31 reproduces, outside the white light imaging planes, an actual image of the corresponding hidden element, generally much larger than the size of the element (e.g., a 0.75 mm diameter element will have an actual image size at 250 mm) 25 mm, at a distance of 100 mm approximately 15 mm). The small spatial extent of each element helps to ensure the invisibility of the device except when it is illuminated by coherent light.

As can be seen in Fig. 3, six discrete points 2 in the form of points are arranged in pairs, each pair contributing to the reproduction of the respective hidden image 7, 8, 9. Points 10, 11 form the first image reproducing pair 2, points 12, 13, a second pair reproducing the second hidden image 8 and points 14, 15 form a third pair reproducing the third hidden image 9.

Since the hidden images 7, 8, 9 are formed from a normal image plane and at a distance from the device 1 where they are in focus, they are invisible to an observer under normal white light illumination.

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Suitably, the discrete sections 2 are positioned close enough to each other to be illuminated by a single conventional beam of laser beams, typically 3 mm in diameter.

Note that, unlike earlier systems, since individual elements visible under laser illumination are placed on small areas on the substrate, the beam cone angle to produce the image is small - this provides a very wide depth of field to produce an approximately in-focus image visible under laser illumination and allows this image on the screen to be viewed relatively close to the substrate (approximately 50 to 75 mm, if required) to give a high brightness element with a narrow viewing angle and a small a flat image area keeps this image well hidden. This contrasts with other known laser-visible systems where the hidden image is spread over a larger area and where the compromise between keeping the image close to the medium and sufficient brightness results in the hidden image becoming easily visible in the light cone and because In the near plane, a variety of reproduction angles are required, greatly degrading any superimposed holographic image, while the technique disclosed here completely places the laser-visible hidden element in place and thus avoids any disruption to all other aspects associated with the security hologram.

Note that in a preferred embodiment, each of the elementary laser verifiable elements of the holographic structure producing an optically variable effect is a hologram displaying two different images in two different focal planes, one of which (white light image) is a focal plane close to the plane of the hologram displayed. where the elemental element is directed to show a visually recognizable graphic element to the hologram observer, while the second focal plane is where it would normally be possible to make a visible projected "rainbow slit" in the embossed rainbow hologram. In this case, elementary holograms in coherent laser illumination reconstruct a simple graphic element such as a letter or shape - this laser-verifiable hidden off-plane element is visible only in coherent (laser) illumination and otherwise is a "white light" for normal viewers spotlight, room lighting or daylight, invisible.

It is important that the reproduced element of each individual graphic element of the hidden images 7, 8, 9 is almost indistinguishable from a colored reproduced element of both a simple folding grid element and a simple lenticular holographic element (e.g., a very short rainbow holographic slit reproducing the viewer in visual conditions). characteristic reproduction of the pure bending grid), which makes the color reproduction and the apparent movement characteristics of the laser-verifiable area almost indistinguishable from the standard holographic movement element. This then effectively serves to conceal the presence of another laser-readable and verifiable message. This is in stark contrast to earlier, laser-verifiable holographic elements, as can be seen in the graphics used (for advertising). These other systems use a number of methods that are at a lower level than the new system described herein, which has a number of distinct and important advantages over previously used techniques. Some earlier methods superimpose a laser-verifiable (or machine-verifiable) image over the entire hologram or large area of the hologram, so they degrade the visual image by creating something that appears at a certain angle as "noise" reproduction. These systems also tend to reproduce in a coherent light a less bright laser-visible image, since the decomposed image is much more susceptible to disruption of surface roughness (eg for hot stamped films) or to surface curl (eg for labels), causing Blurring of the image off-plane due to small angular changes in the direction of image reconstruction caused by planar inequality below 50. Often, the machine-readable elements, when placed on a hologram or bending surface, are very conspicuous due to the relatively large amount of information stored on the laser verifiable element and produce a large reproduction angle and a diffuse and dull white color of the reconstructed image compared to more saturated diffraction colors and thus make the presence of the additional element obvious. This often results in a gradual deterioration of the element at

Production due to the high spatial bandwidth in this area, creating non-linearities and reproduction and noise problems in terminal equipment - this relatively large amount of information stored by other systems tends to require a large number of different superimposed spatial frequencies that tend to compete resulting in edge competition, saturation of the environment, resulting in a less efficient laser verifiable element with increased noise. These manufacturing issues do not give rise to any problems in this new system, as each laser-visible element has been divided into individual small areas containing a limited number of spatial frequencies much similar to that of the holographic areas, ensuring ease of manufacture and minimizing manufacturing deterioration.

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Unlike these earlier systems, the laser verifiable system presented here has several distinct advantages:

First, each individual laser-verifiable element in the present system is located on small areas (e.g., a dot), which means that distortion in the reconstructed image is minimized due to the unevenness of the substrate or the roughness of the paper, thus providing a laser-visible image of higher quality. , with less distortion and less noise due to surface irregularities and easier to verify under coherent lighting.

Secondly, each laser verifiable element contains only a single simple graphic character (eg a letter) as a laser verifiable element of the entire message. This keeps the microstructure of each individual laser verifiable element expressed in units of spatial bandwidth as simple as possible (eg minimizes the number of spatial frequencies to minimize edge competition). This desired reduction in spatial frequency bandwidth allows the visual element to be reproduced in white light, which seems virtually indistinguishable from the diffraction grating element, as it offers substantially saturated color reproduction (not diffuse color reproduction), and this also allows the element to be more efficiently embossed. and to be less sensitive to noise bound during the embossing process due to the saturation of the environment, which occurs faster for lower brightness in more complex optical microstructures.

Third, placing simple graphics at each laser verifiable point, but the subsequent use of different points that reproduce in very different directions for the other features of the message, makes the feature more resistant to lack of flatness and microscopic surface roughness by allowing individual features to be In the laser-visible element, they are angularly and spatially well separated to prevent overlapping.

Fourth, a preferred arrangement of laser verifiable dots or graphic means means to use a certain distance between these graphic elements so that the point size of a typical laser pen illuminates only one element at a time to carry each laser-visible feature, thereby providing the brightest laser-visible feature for each. omitting the slightly different reproduction angles that would be possible if multiple elements corresponding to the same laser-visible feature were illuminated, while repeating laser-verifiable elements in sets or pairs facilitates alignment and easy readability without accurate alignment by ensuring that that, for example, in non-boundary applications, one of each type of laser verifiable feature is illuminated at each individual reading time and also means that each laser-visible feature is repeated at least once to more resistant to, for example, local wrinkling, scratching or scratching of the surface, thus providing better laser verification of old or wrinkled stickers or documents such as banknotes.

This system is also safer than the prior art because it is better disguised than a machine-readable security hologram element and is also more difficult to counterfeit for an organization skilled in holographic and diffraction procedures and plays a role as a publicly recognizable diffractive security device. The following advantages are explained. Said element is better disguised in the security hologram because, firstly, it produces a cleaner diffractive color than other earlier laser-visible elements and thus appears very similar to the other surface diffraction gratings and lenticular elements in the hologram, thereby being a set and presence of holographic elements effectively masked. This element can also be additionally disguised in a security hologram, either in a particular structure or as a spatially separated area in the form of a set of elements or graphics providing a publicly recognizable seemingly moving element that is displayed to the viewer when the hologram is tilted, for example rotation, shape change, image change or linear movement. Thus, this new security element acts as a publicly recognizable device due to the nature of possible apparent movement elements consisting in the technique of angular separation of laser-10 verifiable reproduction in separate different directions attributed to separate spatially different areas.

Figure 5 shows a second embodiment in which the security device is implemented as a single point structure 20, which structure is formed as part of a series of points defined by surface grating elements in the form of lenticular continuous strips. When this device rotates in direction 21 under white light illumination 22, the surface grating elements including the structure 20 cooperate with each other to form an image of a moving point. The structure 20 itself consists of four parts 23 to 26, which are formed of pairs 23, 25, and 24, 26, so that when tilted by the device under white light illumination, they provide a switching pair of images as shown in items 27,28.

In addition, each sector 23 to 26 is also constructed in this way so as to reproduce the respective hidden image 29, 30 under laser illumination 31. As can be seen in Fig. 5B, the pairs of sectors 23, 25 produce the hidden image 30 and the pairs of sectors 24, 26 creates a hidden image 29.

In some cases, the structure 20 could be used by itself. Creating elements of a machine-readable element at the optical microstructure manufacturing stage is also more difficult than prior art devices, since it requires the creation of several separately focused graphical elements in or near the visual hologram image plane reproducing in several different diffraction directions to ideally to produce an apparent movement effect or to produce variation effects upon tilting, and also to produce a self-sharpening, laser-visible image along these reproduction directions, which will only be seen when illuminated by coherent light. The formation of this element would typically be accomplished using conventional holographic techniques, typically in the H1-H2 arrangement, and then instead of using a short rainbow blast 35 to project an elemental image, the rainbow slit is instead formed into a shape designed by a laser visible graphic element. This would then be repeated for each of the several graphic elements, each formula comprising several motion elements and at least two separate laser-verifiable elements, preferably a plurality of these elements. A useful number of 3 or more pairs or sets of individual graphic elements or dots is useful as it is at the level of complexity of the creation and complexity of laser verifiable elements where other techniques are beginning to suffer from deterioration and it is also a useful number of discrete elements useful a complex, visual, publicly recognizable movement element forming part of the visual imaging hologram or other diffractive security devices as appropriate.

It is a useful feature against potential counterfeiters using commercially available so-called "dot matrix" machines that expose the photoresist substrate to two interfering laser beams to form a dot grid and then move this pattern gradually between exposures to create a matrix of grid inscriptions in step-and-repeat computer control (machines available on the market and in literature from, e.g., Dimensional Arts and Ahead Optoelectronics Inc.). The novel security device disclosed herein is a useful anti-counterfeiting device using such point matrix systems, since this device allows a surface-simple, publicly recognizable visual holographic device in which the visual pattern shows a simple moving element

-9C7. 301895 B6 designed for direct public recognition, had a significantly elevated, hidden, laser verifiable security feature, which is easily displayed to the skilled inspector using a laser pointer and a simple screen to reproduce and validate the laser-visualized message. In this case, although the visual movable element can be falsified by the dot matrix pattern, laser visualized off-plane elements for coherent observation could not be copied by a dot matrix system that can only provide a pure reproduction of the diffraction grating (in this case it would be best in the form of a visual graphic for a laser-visible element of point or continuous graphics, since any attempt to copy both the graphic and the dot matrix system would be extremely difficult, requiring the decomposition of the food to the discrete points and reproducing each in different directions laser-visualized elements, although this would be very and perhaps unreachable in terms of spatial and angular resolution for most existing dot matrix systems, and would be difficult to reproduce for other security imaging systems. diffraction grating techniques such as grids based on a combination of standard 15 diffraction patterns such as 'Kinegram' or those based on electron beam recording techniques such as 'Exelgram' and the level of control and complexity would exceeded the capabilities of commonly equipped holographic laboratories, as this would normally be one of the components of a security holographic image containing many other elements.

Most preferably, the device is holographically formed into a photoresist to form a surface relief pattern suitable for the electroforming of a metal backing mold for later stamping. In making the hologram, variations of the known H1 H2 type process could be used to create a surface relief hologram where this device is optionally combined with a 2D / 3D (two-dimensional / three-dimensional) or 3D (three-dimensional) or stereogram or any other diffraction grating or a diffractive security device known in the art. Once the laser verifiable element is reconstructed using coherent laser illumination, the graphical information it is composed of comes into focus or is displayed on the same plane as the Benton iridescence, which are reconstructed in a similar manner when the visible main hologram is illuminated by the same source coherent light.

The surface embossed hologram would then be copied by known galvanoplastic techniques, as known in the art, to make metal copies and hence holographic embossing inserts may be used to emboss said device by a known holographic or diffraction embossing method for optical microstructures. These devices would then be incorporated into stickers, stickers on which there would be obvious falsification, hot stamped foils and similar materials used for the bulk replication of optical security elements, which would then be affixed to valuable documents, plastic cards and valuable goods. .

One aspect that is normally present and advantageous in the practice of the present invention is that the laser verifiable element of the present invention, when recorded as part of a security hologram or diffraction grating or the like, has a spatial frequency of the diffractive carrier grating preferably lower than the holographic edge structure. This is advantageous when reading a laser verifiable element using a laser pointer or similar source, since inexpensive laser sources are (today) almost always laser devices of red color, since the laser verifiable element will bend the red laser light at a smaller angle than the visual holographic structure, thereby angularly separating the laser verifiable element from the visual security hologram to make observation of the laser verifiable element easier. It is therefore advantageous from an authentication point of view to record a laser-visible element on a coarse diffractive structure (i.e., a smaller spatial frequency on a carrier grid) than the accompanying visual photographic element, so as to provide angular separation . This technique of using a coarse bending grid for a concealed (ie machine verifiable) element means that it is often the least scattering feature on the security device that helps minimize image blur during reproduction due to small deviations of the angles bent on the various surfaces of the device due to the roughness of the substrate. Thus, the use of this smaller diffraction angle for the laser verifiable element ensures that diffracted reproductions from the laser verifiable element from all components of the holographic or diffractive security device are least disturbed by the roughness of the substrate.

Referring to Fig. 4, one method for incorporating this additional machine-readable element would be to record a second separate H1 60 (Fig. 4A) corresponding to different image areas for the laser-verified element, say 3 image areas recorded in 3 areas 60A, 60B, 60C belonging to H1 instead of the conventional masking techniques of the iris slit H1 used, the surfaces H1 would be masked in the shape of a desired, laser verifiable element. This H160 could then be used in a well known H1-H2 sequence to transmit a laser verifiable image to the image plane of the H2 61 hologram (FIG. 4B). This would then create a hologram H2 as a rule in a photoresist comprising in the visual image plane a laser verifiable element animated according to the directions of diffraction as defined by the initial design H1 as a laser verifiable element. Using a smaller reference beam angle than any accompanying visual security hologram or diffractive security device would ensure that the laser verifiable element is recorded with a coarser diffraction grating density than the visual diffractive security device. Subsequently, this image could then be combined with the visual security hologram by recording the second hologram H2 on the photoresist from a separate H1 corresponding to the desired visual security image. The photoresist plate would then be developed in the usual manner to form a surface relief hologram. Other production methods are also likely, such as creating a single complex composite H1 containing all elements of both the visual hologram and laser verifiable areas recorded on separate areas with a single transfer recording step for the hologram H2.

Other alternative and equally practicable techniques for creating a laser verifiable feature and 2D / 3D (two-dimensional / three-dimensional) security holograms could include using masks to define visual pixels on the image plane hologram and using appropriately shaped masked diffuse or lenticular diffusion sheets to create an object beam with another separate reference beam, as is known in the art,

Another technique of imaging would be to create a single main hologram of the laser verifiable element, copy it to the metalloid by electroplating and then use mechanical recombination techniques (ie selective flat embossing) to incorporate the element into a security hologram or purely diffractive device, such as Kinegram and Exelgram to increase security on these devices.

Also note that, although the most common use of this technique will be in the form of a surface embossed optical microstructure, such a laser verifiable element as disclosed herein could be used in a bulk holographic security device using recording materials such as silver halide emulsions, Dichromate-treated gelatin and holographic photopolymers (such as manufactured by, eg, I. Dupont, Holographics Division and Polaroid Corporation, Holographics Division) using reflective holography as known in the art (eg G. Saxby, "Practical holography", Prentice Halí ).

In this case, the design and manufacturing techniques would be different in detail. However, the principle of creating an improved, incoherent laser illumination of the hidden element for multiple small graphics remains valid, also used to create an apparent motion effect for public recognition, ie using several holographic elements having both a visual graphic image in the image plane for visual authentication, such as a shape or graphic, as well as a certain graphic shape in an off-plane element forming a laser verifiable element that is visible only in laser light.

In the figures we have described so far, the security device reproduces a number of small dots when illuminated by white light. Giant. 6 illustrates an example in which structure 70 reproduces graphic indicia, in this case NAME, typically under sequence in the name of the device under white light illumination, while laser illumination 6 reconstructs the hidden CODE indicia in another plane as shown below. 71.

Fig. 7 is a modified example corresponding to Fig. 6, in which bar code 72 is reconstructed as a hidden image in laser illumination. Each part of the structure generating one of the letters NAME under white light illumination corresponds to a corresponding portion of bar code 72.

Claims (19)

PATENT CLAIMS A security device (1) comprising an optically variable effect generating holographic structure, characterized in that said holographic structure has at least two discrete sections (2) that generate an optically variable image (3) in response to white light illumination (22, 51) 4, 5), comprising at least two defined graphical elements positioned on or near the image plane of the security device (1) and which, in response to coherent illumination (31), generate at least two discrete hidden images (7, 8, 9), in the form of indicia whose image planes are located at a distance from the actual plane of the security device (1), the hidden images (7, 8, 9) being reconstructed at different angles to the perpendicular to the substrate supporting the security device (1) hidden images (7, 8, 9) spatially separated on their image plane, these hidden images (7, 8 9) invisible when illuminated by white light (22, 51). Security device (1) according to claim 1, characterized in that the optically variable effect generating structure produces, in response to illumination with white light (22, 51), an optically variable image (3, 4, 5) which, when tilted (50) ) of this device moves. Security device (1) according to claim 1 or claim 2, characterized in that the optically variable effect generating structure is formed as a single continuous structure (20). Security device (1) according to claim 3, characterized in that each element of the structure producing a holographic, optically variable effect has a maximum lateral dimensional dimension not exceeding 3 mm and preferably not exceeding 1.5 mm. Security device (1) according to claim 3 or claim 4, characterized in that a set of pairs or sets of at least three of said discrete sections (2) is provided, wherein each element of a particular pair or set is arranged to form in response to coherent lighting (31) the same hidden image (7, 8, 9) as the other element (s) of the pair or set. Security device (1) according to any one of claims 3 to 5, characterized in that said single continuous optically variable effect generating structure (20) is located in a set of other optically variable effect generating structures, the one and the other optically generating structures the variable effect when the substrate is tilted (50) under white light illumination (22, 51), interacting to produce a moving image effect. -12 GB 301895 B6 Security device (1) according to claim 1 or claim 2, characterized in that the discrete sections (2) of the optically variable effect structure are formed as discrete areas spaced apart. Security device (1) according to claim 7, characterized in that it comprises a set of pairs or sets of guided surfaces, each element of the pair or set having the same structure for displaying the same image in visible light. Security device (1) according to claim 7 or claim 8, characterized in that each surface has a maximum lateral dimension not exceeding 3 mm and preferably not exceeding 1.5 mm. Security device (1) according to any one of the preceding claims, characterized in that the optical variable effect generating structure is in the form of a diffraction grating or a holographic structure, such as a security hologram, Security device (1) according to claim 10, characterized in that the part of the structure that additionally responds to coherent illumination (31) has a lattice frequency lower than that part of the structure that responds to white light illumination (22, 51). Security device (1) according to any one of the preceding claims, characterized in that the optically variable effect generating structure is a surface relief structure. Security device (1) according to any one of the preceding claims, characterized in that the hidden images (7, 8, 9) comprise graphic elements, alphanumeric characters, logos or machine-readable patterns such as bar codes. Security device according to claim 13, characterized in that each discrete section (2) forms a hidden image (7, 8, 9) defining a portion of the machine-readable pattern. Security device (1) according to any one of the preceding claims, characterized in that the discrete sections (2) have substantially the same shape. Security device (1) according to any one of the preceding claims, characterized in that the discrete sections (2) have a simple geometric shape, in particular a circle, square or rectangle shape. Security device (1) according to any one of claims 1 to 15, characterized in that the discrete sections (2) are shaped as graphical indicia. Security device (1) according to claim 17, characterized in that these discrete sections (2) define alphanumeric characters. Security device (1) according to any one of the preceding claims, characterized in that the device is holographically formed by arranging the transmission of a Benton type na1 to H2 A document or valuable item provided with a security device according to any of the above claims.